Portable high energy gamma ray imagers (original) (raw)
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A high energy gamma camera using a multiple hole collimator and PSPMT
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
A high energy gamma camera using a parallel hole tungsten collimator and a 7.62 cm square Position Sensitive Photomultiplier Tube (PSPMT) has been assembled and tested. The measured energy resolution is 12-20% FWHM for 137CS (662 keV) gamma rays, and 17-23% FWHM for 57 Co (122 keV). The measured spatial resolution measured is 2.8-3 .2 mm for 122 keV and 3.4-5 .3 mm for 662 keV. The variation in the energy and spatial resolution is due to the continuously varying gain across the PSPMT. Measured energy spectra and images obtained are presented.
Evaluation of the next generation gamma imager
2013 3rd International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications (ANIMMA), 2013
Towards the end of their life-cycle, nuclear facilities are generally associated with high levels of radiation exposure. The implementation of the ALARA principle requires limiting the radiation exposure of the operating people during the different tasks of maintenance, decontamination and decommissioning. CANBERRA's latest involvement in the provision of nuclear measurement solutions has led, in the framework of a technology transfer agreement with CEA LIST, to the development of a new generation gamma imager. The latter, which is designed for an accurate localization of radioactive hotspots, consists of a pixilated chip hybridized to a 1 mm thick CdTe substrate to record photon pulses and a coded mask aperture allowing for background noise subtraction by means of a procedure called mask/anti-mask, which greatly contributes to the reduced size and weight of the gamma imager as gamma shielding around the detector is less required. The spatial radioactivity map is automatically superimposed onto a pre-recorded photographic (visible) image of the scene of interest. In an effort to evaluate the performances of the new gamma imager, several experimental tests have been performed on a industrial prototype to investigate its detection response, including photon sensitivity and angular resolution, over a wide energy range (at least from 59 keV to 1330 keV). The impact of the background noise was also evaluated together with some future features like energy discrimination and parallax correction. This paper presents and discusses the main results obtained in the above experimental study. A comparison with Monte Carlo simulations using the MCNP code is provided as well.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
We are designing and building a compact gamma camera using a semiconductor hybrid pixel detector, for Tc-99m 140-keV imaging of sentinel lymph nodes during radio-guided surgery. In order to perform preliminary evaluations on the spatial resolution attainable with different collimators, we used the Medipix1 readout chip, bump-bonded to a silicon pixel detector (300 mm thick, 64 Â 64 pixels, 170 mm pixel pitch, 1% detection efficiency at 140 keV). In this work we tested its performance with a knife-edge 0.35 mm pinhole collimator. Imaging results obtained with a 122 keV Co-57 gamma source show an on-axis system spatial resolution of 0.8 mm (resp. 1.8 mm) at 10 mm (resp. 40 mm) from the collimator face. The collimator efficiency was 2 Â 10 À4 at 10 mm, reducing to 3 Â 10 À5 at 40 mm from the collimator face. This gamma imaging system is compact, can be made hand-held and provides live-time imaging. It will have an acceptable detection efficiency when the Medipix2 chip will be available, in the next future, bonded to a CdTe pixel detector.
Characterization of performance of a miniature, high sensitivity gamma ray camera
IEEE Symposium Conference Record Nuclear Science 2004., 2004
A compact, hand-held gamma camera with excellent intrinsic and extrinsic performance has been developed for the rapid identification and localization of the sentinel lymph node during the surgical staging of cancer. A goal for this device is an image acquisition time of five seconds to allow the surgeon to easily search for points of interest without excessive motion blurring. The camera comprises a 5x5 cm 2 field of view NaI (Tl) pixellated crystal array, a high sensitivity (2.0 cm thick) hexagonal parallel-hole collimator, a position sensitive photomultiplier tube (PSPMT), and a novel highly multiplexed electrical readout. The good intrinsic energy resolution (12.3±2.6%) resolution, extrinsic sensitivity (5 cps/µCi with 24% energy window) and extrinsic spatial resolution (1.6+/-0.02 mm at 0.5 cm) facilitate rapid identification of a hot node.
Performance Characterization of a Miniature, High Sensitivity Gamma Ray Camera
IEEE Transactions on Nuclear Science, 2007
A compact, hand-held gamma camera with excellent intrinsic and extrinsic performance has been developed for the rapid identification and localization of sentinel lymph nodes during the surgical staging of cancer. The camera comprises a 5 5 cm 2 field of view NaI (Tl) pixellated crystal array, a high sensitivity lead (2.0 cm thick) hexagonal parallel-hole collimator, a position sensitive photomultiplier tube (PSPMT), and a novel highly multiplexed electrical readout. The intrinsic energy resolution (12.1 2.0%) at 140 keV including edge crystals, extrinsic sensitivity (5 cps Ci from 1-5 cm with a 24% energy window) and extrinsic spatial resolution (1.81 + 0.1 mm at 0.6 cm) facilitate rapid identification of a radioactive node. Using a node phantom we performed an ideal observer study to estimate the detectability of small spheres in the range of 3 mm to 8 mm with different exposure times. With a 5 seconds exposure the camera can detect a 3 mm diameter sphere at a depth of 3.6 cm containing 1 Ci of Tc-99m within a cold background, and a 4 mm diameter sphere containing 2 Ci at 2.6 cm depth within a warm background ( 10:1 contrast) with a 5 second exposure duration.
LaBr 3:Ce scintillation gamma camera prototype for X and gamma ray imaging
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007
LaBr 3 :Ce has been showing very promising characteristics as gamma ray imager and spectrometer. In particular its excellent energy resolution values (6% at 140 keV and $3% FWHM at 662 keV), obtained when coupled to a PMT, make it the major competitor of semiconductor detectors working at room temperature. In order to improve its imaging performances, the LaBr 3 :Ce can easily work as continuous detector allowing sub-millimeter spatial resolution values at 140 keV photon energy when coupled to a Position Sensitive PMT. Further interesting characteristics like a short scintillation decay time (16 ns), a very high light yield (63 000 photons/MeV) and a low afterglow are attracting the scientific community for the potential improvement of a wide range of applications in medicine like PET, SPECT and CT instrumentation. In this paper, we present some preliminary imaging results obtained by coupling H8500 Hamamatsu Flat Panel PMT to two LaBr 3 :Ce crystals with 50 Â 50 mm 2 area, 5 and 10 mm thickness respectively. With the aim to propose a single detector able to combine functional information, for example from Single Photon Emission technique, with the morphological ones from X-ray imaging the spatial resolution results obtained in the energy range between 30 and 302 keV are analyzed and discussed. We obtained very interesting spatial resolution results for gamma ray energy value greater than 60 keV (better than 1 mm, intrinsic value), while in the energy range proper to X-ray applications, like RX-Mammography (about 30 keV), the spatial resolution values resulted about 2 mm. r
New Devices for Imaging in Nuclear Medicine
Cancer Biotherapy & Radiopharmaceuticals, 2004
Pinhole gamma camera imaging offers the ability to obtain high resolution images from single gamma ray emitting radiotracers playing a reasonable tradeoff between very small field of view (FoV) and sensitivity. On the other hand the total spatial resolution of a pinhole imaging device is predominantly affected by the detector intrinsic spatial resolution for reduced magnification factors. To design very compact pinhole SPET scanners with very high intrinsic spatial resolution, authors investigated a miniature gamma camera based on the newly developed Hamamatsu H8500 flat panel photomultiplier. The PSPMT was coupled to the following scintillation arrays: CsI(Tl) array with 0.2-mm, 1-mm, 1.4-mm pixel size and NaI (Tl) with 1-mm pixel size. The imaging performances were evaluated by 57 Co spot and flood irradiations. NaI(Tl) array shows a better pixel identification for 1 mm pixel size, proving to be a good candidate to make a large area photodetector based on multi PSPMTs closely packed. Although CsI(Tl) array had the smallest pixel size, the low light output limited the best intrinsic spatial resolution to about 0.5 mm.
A novel compact gamma camera based on flat panel PMT
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
Over the last ten years the strong technological advances in position sensitive detectors have encouraged the scientific community to develop dedicated imagers for new diagnostic techniques in the field of isotope functional imaging. The main feature of the new detectors is the compactness that allows suitable detection geometry fitting the body anatomy. Position sensitive photomultiplier tubes (PSPMTs) have been showing very good features with continuous improvement. In 1997 a novel gamma camera was proposed based on a closely packed array of second generation 1 in PSPMTs. The main advantage is the potentially unlimited detection area but with the disadvantage of a relatively large non-active area (30%). The Hamamatsu H8500 Flat Panel PMT represents the last generation of PSPMT. Its extreme compactness allows array assembly with an improved effective area up to 97%. This paper, evaluates the potential improvement of imaging performances of a gamma camera based on the new PSPMT, compared with the two previous generation PSPMTs. To this aim the factors affecting the gamma camera final response, like PSPMT gain anode variation and position resolution, are analyzed and related to the uniformity counting response, energy resolution, position linearity, detection efficiency and intrinsic spatial resolution. The results show that uniformity of pulse height response seems to be the main parameter that provides the best imaging performances. Furthermore an extreme identification of pixels seems to be not effective to a full correction of image uniformity counting and gain response. However, considering the present technological limits, Flat Panel PSPMTs could be the best trade off between gamma camera imaging performances, compactness and large detection area. r
Experimental tests of a hybrid pixellated detector for gamma imaging
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
In the framework of the MEDIPIX Collaboration, a hybrid pixel detector has been developed primarily for X-ray radiography. This detector consists of a 64 Â 64 pixel photon counting chip (PCC), bump bonded to a 200 mm thick GaAs substrate. The PCC is optimised for energy depositions in the range of a few keV to a few tens of keV. The aim of this study is to evaluate the detector for applications in decommissioning of nuclear power plants where typical sources have energies in range of a few hundred keV. Tests were realised using a 137 Cs gamma source (660 keV). At this energy, Monte-Carlo simulations predict that, on average, for more than 60% of primary interactions, there is at least one pixel on which the deposited energy exceeds 100 keV. Simulations also allow modelling of the spatial energy spreading. The comparison of the simulation results with experimental data should indicate if there is a significant contribution of electrical cross-coupling between pixels to the cluster size of the detected hits. The results obtained demonstrate promising perspectives for this kind of detector towards gamma imaging applications.
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